With few exceptions, tapered designs for uni-directional (UD) material are currently certified only for balanced and symmetric laminate construction, despite the severe design constraint that 1 angle-ply termination therefore requires a further 3 angle-ply terminations. By contrast, an extensive design space has recently been discovered for tapered UD laminates with single ply terminations, including single angle-ply terminations, representing unconventional laminate designs with unbalanced and/or non-symmetric stacking sequences. Such designs give rise to Bending-Twisting and/or Extension-Shearing coupling:

Extension-Shearing coupling, which arises in unbalanced construction, can be exploited to produce bending-twisting deformation in aircraft wing-box structures when top and bottom skins have identical bias fibre alignment, but equally, this can be eliminated with opposing bias fibre alignment;
Bending-Twisting coupling, which is generally present in symmetric laminate construction, results in weaker compression buckling strength compared to the equivalent fully uncoupled laminate (with matching stiffness properties), but with potentially stronger shear buckling strength.

Single ply terminations applied to NCF or balanced plain weave materials are equivalent to two adjacent ply terminations in traditional UD materials, and therefore introduce a constraint that may reduce the design space substantially, particularly in ‘thin laminate’ designs. However, this can be overcome by adopting ‘thin-ply’ or ‘spread-tow’ technology, which will allow an exponential increase in tailoring opportunities by bringing design flexibilities, found only in traditionally thick laminate construction, into the thin laminate domain.

Thin-ply technology will, for instance, offer the prospect of a repeating 8-ply NCF laminate, with a similar thickness to that of a single ply of traditional UD material. This design also follows the repeating bi-angle philosophy, possessing Extension-Shearing and Bending-Twisting coupling, but now with immunity to thermal warping distortions, which are eliminated in bi-angle laminates only when the number (r) of repeats becomes very large.